This invention relates to catalyzed chemical conversion processes in which solid catalysts become deactivated through the accumulation of reaction product residue or other solid contaminant, e.g., "coke" or other carbonaceous residue, and in particular, to the reactivation of such catalysts using ultrasonic energy applied to the catalysts after they have become partially but less than completely deactivated due to such accumulated residue.
The use of solid catalysts to effect chemical conversion processes such as cracking, reforming, isomerization, disproportionation, alkylation, hydration, etherification, etc., is known. These catalysts include non-crystalline or amorphous types such as silica and alumina, and crystalline types such as the zeolites, both of which types can contain one or more other catalytically active species. In use, the catalysts gradually accumulate deposits, or residues, which cover the catalysts' surfaces and/or fill their pores eventually rendering them essentially completely inactive. Thus, at some point during their on-stream life, a period of time which can be just a few minutes in the case of a cracking operation to hours, days or even weeks in the case of some other types of chemical conversions, e.g., olefin hydration to produce alkanol, it becomes necessary to recover the catalysts and to reactivate them. One of the most commonly practiced catalyst reactivation procedures employs a burn-off procedure in which the residues are converted to gaseous carbon oxides and water.
Some types of solid catalysts, however, cannot withstand the high temperatures, generally from about 600.degree. F. to about 1100.degree. F., which are typical of the aforementioned burn-off reactivation procedures. One such catalyst, a boron trifluoride-graphite intercalate which is used in paraffin alkylation, undergoes irreversible damage when subjected to temperatures of this magnitude. Other thermally sensitive catalysts respond in much the same way to the high temperatures of oxidative burn-off operations.
U.S. Pat No. 4,086,184 describes the reactivation of hydrocarbon conversion catalysts employing ultrasonic sound, or insonation, either before or after a conventional burn-off operation. The reactivation procedure of this patent is disadvantageous in requiring separation of the catalyst from the feedstock, reactivating the catalyst and only then resuming the conversion operation. Even when, in accordance with this patent, the ultrasonic insonation is carried out within the conversion zone, i.e., within the reactor, the reactor must first be drained of feedstock and filled with a viscous liquid medium prior to insonation. This, of course, requires an interruption in the operation of the conversion process.